Lord Hamilton of Dalzell

The 4th Lord Hamilton of Dalzell, who has died aged 68, was a hereditary peer with the motto Quis occursabit (Who Will Oppose?) and a strong opponent of the Blair government's alterations to the make-up of the House of Lords.

A natural opponent of bureaucracy, he joined the Conservative Party "awkward squad" on taking his seat after his father's death in 1990 and made his mark opposing the Common Agricultural Policy, leasehold reform and the Maastricht Treaty. He was so exasperated by the party's failure to mount a forceful defence of the hereditary peers that he voted against the Ballot Bill, which offered survival for 92, then refused to nominate himself to be chosen as one of them.

When a life peer and former minister asked why, he replied: "It is a matter of principle. If you knew what that was, you would have done the same."

A 6ft 5in patrician figure, who resented discourtesy and made people of all ranks feel at ease, Hamilton was one of four hereditary peers who petitioned the Queen against the Treaty of Nice on the grounds that it breached the terms of Magna Carta; his pamphlet Manifesto for Sovereign Britain was published by the Freedom Association in 2004.

James Leslie Hamilton was born on February 11 1938 into a family that included a soldier killed fighting for Mary Queen of Scots and another who served with the Scots Greys at Waterloo.

The first Lord Hamilton of Dalzell was a Liberal MP for Falkirk; the second chairman of the Royal Fine Art Commission for Scotland; the third a Lord in Waiting who had been wounded with Coldstream Guards in the Second World War.

Young James, the elder brother of the Tory minister Archie Hamilton (who was created a life peer as Lord Hamilton of Epsom last year), inherited a belief in Christian Science from his mother and a love of gardening from his father.

After Eton he did his National Service in the Coldstreams, contriving as a liaison officer in Germany to sleep in large castles while his commanding officer bivouacked in soggy woods. For a time he drove a truck in a Canadian uranium mine. But when, after that, he had settled down as a gilts broker in London, Hamilton received a telephone call from his mother.

"James, James, the most dreadful thing has happened," she said. "You must come home at once." The devastating news was that he had been left two estates, one in Surrey, the other in Shropshire.

Retiring from the City, he took great care of both, never allowing local planners to force their ideas – which he though excessively rigid – on him, and concentrated on working with charities.

One was Queen Elizabeth's Foundation for Disabled People. The other was the Henry Smith charity, whose decision to sell its 84-acre South Kensington estate for £280 million in 1995 he opposed in the justified belief that it was undervalued.

Hamilton married, in 1967, Corinna Dixon, with whom he had four sons. The eldest, Gavin, who was born in 1968, succeeds to the peerage.